This is one of the functions of the Chevy Volt - "...its internal combustion engine powers an electric generator to extend the vehicle's range as needed. When t

This is one of the functions of the Chevy Volt - "...its internal combustion engine powers an electric generator to extend the vehicle's range as needed. When the engine is running it may be periodically mechanically linked (by a clutch) to a planetary gear set, and hence the output drive axle, to improve energy efficiency." -- from wikipedia page on the Volt